Aircraft fuel tank construction

ABSTRACT

An aircraft fuel tank construction for the type of fuel tank which is fabricated by joining a split cylindrical center section with two conical end sections and which is disassembled during shipment and storage. The center section is joined together by a connecting plate which maintains a gap between the joined ends at a fixed, predetermined width for optimum sealing effectiveness of an interposed elastomeric seal. Owing to the manner of construction, the seal may be seated and then visually inspected for potential leakage before the center section is joined. Leakage at the interface of each end section seal with the center section seal is avoided during expansion or contraction of the center section seal by the center seal being suitably positioned to slide over the end seal during such movement. The tank is free from drag-producing obstructions as all joints are flush with the surface of the tank.

BACKGROUND OF THE INVENTION

This invention relates to an aircraft fuel tank construction and moreparticularly to construction of a fuel tank which is assembled from acylindrical center section, a conical nose section and a conical tailsection, and which is disassembled during shipment and storage.

For military purposes, it is desirable to manufacture lightweightrefueling tanks in sections which can be nested during shipment andstorage for maximum storage capacity but so constructed that they can bequickly and easily assembled in securely connected, fully sealed, liquidtight relationship. To enable the center section, and center sections ofother such tanks, to be nested one within the other and thus form acompact package, the center section is formed with a longitudinal gapthroughout its length. The side walls of the section facing the gap areconnected together and the gap sealed when the center section isassembled with the two end sections. The end sections are sealed attheir juncture with the center section by a circumferential end seal,which is also in sealing contact with the seal for the center section.Such a tank construction is described in U.S. Pat. No. 2,876,923.

There are several problems associated with known tank constructions. Insome tank constructions, the center section is joined by fasteners andthe width of the gap is not fixed but dependent on the degree to whichthe fasteners are tightened. With this type of construction, the centersection seal may either be overcompressedor undercompressed byimproperly torquing the fasteners, which may make the seal ineffective.Another problem is that overtorquing the fasteners by unskilledpersonnel may cause the center section seal to elongate and resultinglycompress the end seals at their interface with the center section seal,thereby resulting in a fuel leakage path at this point. Similarly,contraction or expansion of the center section seal due to temperaturechanges may also cause the tank to leak at the interface of the sealsbecause of the relative movement between the seals.

Another problem associated with known fuel tanks is that often thecenter section seal cannot be visually inspected after the seal isseated. As a consequence, an improperly seated seal cannot be detecteduntil the fuel tank is filled with fuel and a leak occurs.

Another problem of known fuel tanks is that one or more of the joints ofthe fuel tank may protrude above the surface of the tank causing anincrease in aerodynamic drag.

BRIEF SUMMARY OF INVENTION

Accordingly, it is a broad object of this invention to provide anaircraft fuel tank which may be disassembled and nested during shipmentand storage and which can be easily and quickly assembled in the fieldwith fluid tight integrity by unskilled personnel.

Another object is to provide a means of connecting a center tank sectiontogether whereby in connecting the section, an interposed seal can notbe overcompressed or undercompressed by unskilled personnel.

Still another object is to provide an aircraft fuel tank constructionhaving a gap through the center section of a fixed, predetermined widthfor optimum sealing effectiveness of an interposed, elastomeric seal.

A further object is to provided an aircraft fuel tank constructionwherein expansion or contraction of the center section seal will notadversely affect the sealing integrity of the tank.

Another object is to provide an aircraft fuel tank construction whereinthe seal for the center section of the tank may be seated and visuallyinspected before the section is joined.

Another object is to provide an aircraft fuel tank construction havingan effective sealing interface between the center section seal and theconical end section seals.

Another object is to provide an aerodynamically efficient aircraft fueltank construction wherein all joints are flush with the surface of thetank.

Another object is to provide an aircraft fuel tank which can beeconomically and feasibly manufactured.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

In accordance with these objects, the invention comprises an aircraftfuel tank assembled from three sections: a conical nose section, aconical tail section, and a split cylindrical center section.

The center section is formed with a pair of opposed, recessed, groovedflanges having end walls facing the gap in the section. One of theflanges carries a base plate that extends underneath the gap to thebottom of the opposite flange, thereby forming a three-sided receptaclewith the end walls of the flanges. An elastomeric seal is seated withinthe receptacle to seal the gap. Since the seal is visible when seated,it may be inspected for proper seating prior to connecting the centersection together.

After the seal is seated and inspected, the center section is connectedtogether by a connecting plate having depending tongues which areengaged and interlocked with the grooves on the recessed flanges. Thedistance across opposing tongues of the plate is specificallydimensioned to maintain the gap at a predetermined width for optimumsealing of the interposed seal. Because the flanges are recessed, theconnecting plate is flush with the skin of the tank after being clampedto the center section by mounting screws or bolts, and thus there are nodrag-creating obstructions at the connection.

The conical end sections of the tank are joined to the center section bya retaining ring clamped over recessed end flanges in a tongue andgroove relationship similar to the manner in which the center section isconnected. The joint for each end section is sealed by a pair of O-ringscarried within channels of a seal retaining ring underlying the joint.Means are provided to prevent the sealing ring from laterally shiftingrelative to the joint.

When the conical end sections are joined to the center section, thecenter section seal is arranged to overlap and to slide over one of theO-rings when the center section seal is contracted or elongated bytemperature differentials, thus avoiding any leakage at the interface ofthe seals. The center section seal also has a rectangular cross sectionat each end to completely seal the housing within which it is enclosedand thereby prevent any leakage through the ends of the seal.

Owing to the simplicity of construction, the tank is particularlyfeasible and economical to manufacture.

The invention accordingly comprises the features of construction,combination of elements and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing in which:

FIG. 1 is a side view of the aircraft fuel tank constituting thisinvention attached to the wing of an aircraft, only a portion of whichis shown;

FIG. 2A is a fragmented cross-sectional view of a known aircraft fueltank, particularly illustrating the interface between the center sectionseal and the conical end section seal;

FIG. 2B is a plan view of the tank shown in FIG. 2A with the tankpartially broken away along the line 2B--2B;

FIG. 2C is a partial cross-sectional view taken along the line 2C--2C ofFIG. 2A, particularly illustrating the leakage path through the conicalend section seal caused by abnormal elongation of the center sectionseal, a problem associated with this type of tank construction;

FIG. 3 is a fragmented plan view of the aircraft fuel tank constitutingthis invention taken where the center section joint intersects theconical nose section with the center section, connecting plate andconnecting ring partially broken away to illustrate the configuration ofthe underlying recessed flanges;

FIG. 4 is a cross-sectional view with the seal in elevation taken alongthe line 4--4 of FIG. 3;

FIG. 5 is a cross-sectional view taken along the line 5--5 of FIG. 3;

FIG. 6 is a cross-sectional view taken along the line 6--6 of FIG. 3;

FIG. 7 is a cross-sectional view with the seal in elevation taken alongthe line 7--7 of FIG. 3; and

FIG. 8 is a perspective view of the center section seal taken at one endthereof, illustrating the configuration of the seal at each of its ends.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring now to the drawings in detail, there is illustrated in FIG. 1a fuel tank 10 comprising this invention. As is typical for such fueltanks, the tank is assembled from three aluminum sections: a centersection 12, a conical nose or end section 14, and a tail or end section16. The tank is usually attached to an aircraft structure 18, only aportion of which is shown, by a pylon or attachment means 20.

As is typical, the center section 12 is formed or rolled into acylindrical configuration with a gap through the length of the sectionto facilitate nesting the section during shipment and storage. The gapis sealed by an elastomeric seal when the tank is assembled as willhereinafter be described. For purpose of description, this seal willhereinafter be referred to as the center section seal.

In FIGS. 2A, 2B, and 2C, a known aircraft fuel tank of the type withwhich this invention is concerned is illustrated for the purpose ofassistance in the description of significant problems associated withsuch known tanks, which problems this invention overcomes. As seen, acenter section seal 22 is clamped between two upright opposing flanges24 attached to the center section. At each end of the center sectionseal, the seal curves downwardly and contacts in sealing relationship anend seal 26. Seal 26, basically an O-ring supported on a seal retainingring 28, seals the rearward end of the joint between the center sectionand the conical end section of the tank. A problem associated with thistype of construction is that if flanges 24 are overtightened orirregularly tightened, center section seal 22 may abnormally elongateand cause excessive downward pressure on the end seal 26. This oftencauses seal 26 to either crack at the interface of the seals or tocreate a void 27 (exaggerated) as shown in FIG. 2C which provides aleakage path for the fuel to seep through the end joint. Similarly,thermodynamic expansion may elongate the seal and cause the leakagepath. Another problem associated with this construction is that the twoupright flanges create an obstruction on the tank and resultingly causean increase in aerodynamic drag.

Applicant's construction, particularly shown in FIGS. 3 through 8,overcomes these problems as well as the other previously stated problemsattendant in the prior art.

As illustrated in these figures, the center section 12 of the tank, asbest seen in FIGS. 3 and 6, is formed with first and second recessedflanges 30, 32, the side walls of which face and define a gap extendingthrough the length of the section. A first of these recessed flanges 30includes a depending bottom plate 34 which extends underneath the gap tocontact the bottom of opposing recessed flange 32 when the flanges aredrawn together as shown. A receptacle is thereby formed between theopposing ends of the recessed flanges and the bottom plate 34. The outersurface of the flanges carries a series of parallel grooves 36 forinterlocking engagement with a connecting plate 38, as will hereinafterbe described.

Before the center section 12 is connected together during assembly ofthe tank, an elastomeric center section seal 40, having a circular crosssection substantially throughout its length, is placed between the sidewalls of the two opposing flanges 30, 32 as shown to seal the gaptherebetween. Bottom plate 34 assists in guiding flange 32 in alignmentwith flange 30 as the tank is drawn together and also functions asbottom support for seal 40.

The center tank section 12 is connected after the tank is drawn togetherby a connecting plate 38 having a plurality of parallel dependingtongues 42 which are interlocked within grooves 36 on the recessedflanges 30, 32. Connecting plate 38, which extends substantiallythroughout the length of the center section, is clamped to the top ofthe recessed flanges by screws or bolts 44 extending through sealedholes in the tank into conventional floating nuts 48 attached to thebottom of the bottom plate 34, only two of such bolts 44 and nuts 48being illustrated for convenience. The distance across opposing tongues42 of connecting plate 38 is calculated to produce a predetermined widthof the gap for seal 40. This gap width is selected in combination withseal 40 to effect an optimum sealing relationship between the end wallsof flanges 32, 34 and seal 40 whereby the seal will effectively seal thegap during all temperature ranges to which the tank is subjected.

Advantageously, after being seated, the seal can be visually inspectedto insure that it is properly seated and not crimped in any manner priorto the installations of the plate. Owing to the tongue and grooverelationship between the recessed flange and the connecting plate andthe camming action between the two as the plate is clamped, installationof the connecting plate also facilitates the alignment of the recessedflanges 30, 32.

As shown in FIG. 8, center seal 40 has a rectangular cross section ateach end to completely fill the gap between flanges 32, 34, bottom plate34, and connecting plate 38 at each end of the center section andthereby prevent any leakage through the end of the seal as willhereinafter be further explained. As should be obvious, the seal has acircular cross section through most of its length to provide voids atthe corners of the gap for the expansion of the seal when it iscompressed.

Flanges 30, 32 are recessed to receive the connecting plate flush withor below the exterior surface of the tank so as not to create anobstruction at the connection which would produce an undesirableaerodynamic drag. For this reason, the heads of screws 44 are alsocountersunk within the connecting plate.

The manner in which the conical nose section 14 is joined to centersection 12 is best seen in FIGS. 3 and 4. Although the following will belimited to the manner in which the nose section is attached to thecenter section, it should be understood that the tail section isattached to the center section in exactly the same manner, but thedescription thereof will be omitted in the interest of brevity.

Center section 12 carries about its circumference at its front and rearends a recessed end flange 50, only the front flange being shown. Asbest seen in FIG. 4, flange 50 is installed over a cylindrical, sealretaining ring 52 having a pair of U-shaped channels 54 housing a pairof O-ring seals 56, 57. Nose section 14 is formed at its open end with acontinuous, recessed flange 58, similar in configuration to flange 50,which is placed over seal retaining ring 52 and butted against flange50, as shown. Both end flanges 50, 58 have parallel grooves 60 abouttheir circumference. To join the end flanges, a split, connecting ring62 having depending parallel tongues 64 is clamped on top of the flangesby sealed, recessed screws or bolts 63, only two of which are shown,which extend into nuts, not shown, attached to the bottom of the sealretaining ring 52. When the ring is installed, tongues 64 of the ringare in interlocking engagement with grooves 60 of the flanges. Similarto the connecting plate 38, connecting ring 62 is recessed flush with orbelow the exterior surface of the tank for reduction of aerodynamicdrag.

When the center section 12 is joined to nose section 14, the first ofsaid O-ring seals 56 bears against the inner circumference of the nosesection 14, thereby sealing the forward end of the transverse jointagainst leakage, and the second O-ring seal 57 bears against the innercircumference of center section 12, thereby sealing the rearward end ofthe transverse joint against leakage.

To facilitate the engagement of the nose section with the retainingring, flange 58 of nose section 14 sweeps outwardly at the bottom endthereof. To compensate for the upward sweep of flange 58, seal retainingring 52 is also formed with an upward slanting wall 66 about itscircumference to mate with the flange.

Seal retaining ring 52 also has lateral restraining means to prevent thering from sliding laterally relative to the transverse joint. Thislateral restraining means is provided by a pair of shoulders 68, 70 onthe circumference of the ring, best seen in FIG. 5. The left shoulder 68as viewed butts the forward end of the recessed flange 50 of the centersection, and the right shoulder 70 butts the rearward end of flange 50.Shoulder 68 prevents the ring 52 from sliding rearwardly, or to theright as viewed, and conversely, shoulder 70 prevents the ring fromsliding forwardly, or to the left as viewed.

The retaining ring 52 and the above described manner of joining the nosesection 14 to the center section 12 are known in the art.

To overcome the problem of excessive elongation (or contraction) of thecenter section seal 40 adversely affecting the sealing integrity of thetank, each end of the center section seal is designed to overlap eachrespective O-ring seal 57 in a sliding, sealing relationship. That is,the center section 12 is positioned so that the ends of the seal aretangent to the outer surface of O-ring seals 57 whereby any contractionor expansion of the center section seal will cause the seal to slideover the seals 57 and not compress or pull away from seals 57.

As best seen in FIGS. 7 and 8, the end 72 of the center section seal isof a rectangular configuration to correspond with and entirely fill thegap formed between the opposing side walls of the recessed end flangesof the center section, and between the connecting plate and bottomplate. This prevents any fluid from seeping through the ends of the seal40 at the interface of seal 40 and seals 57.

From the above description, it should now be evident that a novel andadvantageous fuel tank construction has been provided. Advantageously,the center section is joined with a connecting plate which fixes thewidth of the gap between the side walls of the section and which willnot leave undesirable obstructions that would interfere with the airflow over the tank. Since a predetermined gap is maintained throughoutthe length of the center section, a seal of a selected dimension may beplaced in the gap for optimum sealing effectiveness. Moreover, the sealmay be visually inspected for proper sealing prior to complete assembly.Advantageously, the above is combined with an improved interface of thecenter section seal with each end section seal which permits the centersection seal to contract or elongate without affecting the fluidintegrity of the tank. In addition, the assembly of the tank can beeasily and quickly accomplished by unskilled personnel with reliability,and owing to its simplicity of construction, the tank is feasible andeconomical to manufacture.

While I have typically described a certain embodiment of my invention,it is of course to be understood that the invention is not limited tothat particular embodiment or form, but rather is applicable broadly tonumerous variations falling within the scope of the appended claims.

I claim:
 1. An aircraft fuel tank construction comprising:a. acylindrical center section and a conical end section attached to thefront and rear ends of the center section; b. the center sectionincluding a pair of opposing recessed flanges with side walls defining agap throughout the length of the center section, the outer surface ofsaid flanges having grooves parallel to one another and parallel to theside walls of the flanges, a bottom plate attached to the bottom of oneof said flanges and extending under said gap and in juxtaposition withthe bottom of the other of said flanges, and a flexible center sectionseal interposed between and in contact with the side walls of theflanges for sealing said gap; c. a connecting plate connecting saidflanges together, said connecting plate having depending paralleltongues extending into and interlocked with the grooves of said flanges,and the connecting plate being clamped substantially flush with or belowthe exterior of said tank; d. the center section further including arecessed end flange carried about its circumference at each end thereof,and each of said end flanges having on its outer face circumferentiallyextending parallel grooves; e. each conical end section having arecessed flange carried about its open end, and each of said conicalsection flanges having on its outer face circumferentially extendingparallel grooves; f. each conical section flange lying adjacent centersection end flange at each end of the center section; g. a splitconnecting ring joining said conical section flange and center sectionend flange at each end of the center section, said connecting ringhaving depending parallel tongues extending into and interlocked withthe circumferential grooves of said conical section and center sectionend flanges, and said connecting ring being clamped substantially flushwith or below the exterior of said tank; h. a cylindrical seal retainingring underlying the joint between each conical end section and thecenter section, said retaining rings carrying a pair of O-ring seals forsealing each of said joints, a first of said O-ring seals contacting theinner circumference of said center section and sealing thereby one endof the joint and a second of said O-ring seals contacting the innercircumference of said conical end section and sealing thereby the otherend of said joint; i. interlocking means for interlocking said sealretaining ring against lateral movement with respect to the joint; andj. said center section seal lying in a direction tangent to and insliding contact with the outer surface of the first of said O-ring sealsat each end of said center section, and said center section sealcompletely filling and sealing the gap between the recessed end flangesof the center section at the interface of the seals.